Subcycle-resolved strong-field tunneling ionization: Identification of magnetic dipole and electric quadrupole effects

Interaction of a strong laser pulse with matter transfers not only energy but also linear momentum of the photons. Recent experimental advances have made it possible to detect the small amount of linear momentum delivered to the photoelectrons in strong-field ionization of atoms. Linear momentum transfer is a unique signature of the laser-atom interaction beyond its dipolar limit. Here, we present a decomposition of the subcycle time-resolved linear momentum transfer in terms of its multipolar components. We show that the magnetic dipole contribution dominates the linear momentum transfer during the dynamical tunneling process while the postionization longitudinal momentum transfer in the field-driven motion of the electron in the continuum is primarily governed by the electric quadrupole interaction. Alternatively, exploiting the radiation gauge, we identify nondipole momentum transfer effects that scale either linearly or quadratically with the coupling to the laser field. The present results provide detailed insights into the physical mechanisms underlying the subcycle linear momentum transfer induced by nondipole effects.

Automated summary

This article investigates the linear momentum transfer in the interaction of strong laser pulses with matter. It is found that linear momentum transfer is a characteristic feature of laser-atom interaction. The decomposition of the subcycle time-resolved linear momentum transfer into its multipolar components reveals that the magnetic dipole contribution dominates the linear momentum transfer during the dynamical tunneling process, while the postionization longitudinal momentum transfer is primarily governed by the electric quadrupole interaction. Additionally, non-dipole momentum transfer effects, which scale linearly or quadratically with the coupling to the laser field, are identified using the radiation gauge.